A far infrared ray radiating material is indicative of a substance which radiates far infrared rays at a high rate around room temperature. This material radiates far infrared rays having a wavelength range of 6-12 .mu.m which corresponds to the inherent vibrating frequencies of the molecules of living creatures, therefore keeping living creatures in active state, as well as preventing living creatures from decomposition.
After discovering the effect of the far infrared ray radiating materials, methods of manufacturing food containers containing far infrared ray radiating ceramics are being developed.
Japanese Patent laid-open No. 87-164509, 89-150527, 90-53838, and 90-138367 are the examples of the conventional techniques which attempt to maintain the freshness of foods by mixing ceramics in thermoplastic or thermoset resins.
Above patents were successful in maintaining the freshness of foods by utilizing the far infrared rays radiated, but they can not provide transparency to the products due to the intrinsic properties of the resin itself or due to the insufficient compatibility between the added ceramic and the base substance which limits the application of the products where transparency is required.